Protection from unauthorized file upload in product/product/upload

OpenCart has no checks from unauthorized uploading files via the product/product/upload action. There is only a test for mime type of the uploaded file, but the page with the following code allows you to upload any number of files on the server, filling all available space.
```html
<html>
<body>
  <!-- Change action for your OpenCart location -->
  <form action="http://localhost/opencart/index.php?route=product/product/upload" method="post" enctype="multipart/form-data">
    <input type="file" name="file">
    <input type="submit" value="Submit File">
  </form>
</body>
</html>
```
This code adds a check for compliance with csrf parameter.